Copper-lead alloy

ABSTRACT

A METHOD OF MAKING A HOMOGENEOUS COPPER-LEAD ALLOY HAVING A FINE AND EVEN DISPERSION OF THE PHASES, AND THE ALLOY AND ITS USES, WHEREIN THE METHOD COMPRISES ADDING AN EFFECTIVE AMOUNT OF A HOMOGENEITY PROMOTER TO A MIXTURE OF MOLTEN LEAD AND COPPER. THE PROMOTER COMPRISES ELEMENTAL CARBON AND A RARE EARTH COMPOUND. AN EXAMPLE OF THE RARE EARTH COMPOUND IS A RARE EARTH FLUOROCARBONATE SUCH AS CERIUM FLUOROCARBONATE.

March 13, 1973 c. E. LUNDIN COPPERLEAD ALLOY Fild Aug. l0, 197C United States Patent Office 3,720,507 Patented Mar. 13, 1973 3,720,507 COPPER-LEAD ALLOY Charles E. Lundin, Evergreen, Colo., assigner to Colorado Springs National Bank, Colorado Springs, Colo. Filed Aug. 10, 1970, Ser. No. 62,338 Int. Cl. C22c 9/08, 11/00 U.S. Cl. 75-135 12 Claims ABSTRACT F THE DISCLOSURE DISCLOSURE OF THE INVENTION This invention relates to alloys and in particular to copper-lead alloys and methods of making them and different uses thereof. The term homogeneous is used herein to refer to an improved alloy having a line and even dispersion of the phases.

Attempts to produce homogeneously dispersed copperlead alloys have been made in order to provide such alloys which have high thermal conductivity, low electrical resistivity and a low coeicient of friction. These properties are highly desirable for metals used to make bearings or as a bearing material and as a dry lubricant o-r as an additive to liq-uid or viscous lubricants made of petroleum or vegetable bases. However, many problems exist in attempting to make homogeneously dispersed copper-lead alloys. The basic problem with these alloys is the prevention of massive separation and segregation of the copper and lead. This tendency to separate aud segregate increases as the lead content rises in the copper-lead alloy. Another problem associated with the use of copperlead alloys is that even if there is initial homogeneity, under high stress and temperature conditions, the lead has a tendency to separate and segregate from the copper. A further problem associated with copper-lead alloys is that the lead tends to segregate from the copper when it is being remelted and recast into other shapes and forms.

It is therefore an object of the present invention to provide a copper-lead alloy with improved homogeneity of the phases.

Another object of the present invention is to provide a homogeneous copper-lead alloy in which segregation of lead from copper is reduced on remelting.

Yet another object of the present invention is to provide a homogeneous copper-lead alloy which is useful for production of bearings and a bearing material.

Yet another object of the present -invention is to provide a process for making the improved copper-lead alloy of the present invention.

These and other objects will be apparent from a reading of the specification and claims of this application.

Briefly, in accordance with the present invention, the foregoing and other objects are accomplished by adding effective amounts of a homogeneity promoter to the molten metal. The promoter comprises elemental carbon and a rare earth metal compound which reacts under the molten conditions present during the alloying and casting of the copper and lead. The mechanism provided by the promoter apparently is one of inoculation of a line dispersion of the lead particles in a copper matrix. Examples of such compounds are the uorocarbonates, carbonates and oxides of the rare earths.

Copper-lead alloys are produced according to the present invention in varying proportions of copper and lead. The proportions may be varied as desired and as the specifc application dictates. It has been found that alloys of substantial utility are those which contain 5% to 55% lead and to 45% copper. The problem of separation and segregation of the lead and copper is greatest with a high lead content. The promoter of this invention therefore provides its greatest utility at lead contents of from 20 to 45%. If the lubricating qualities of the alloy are to be increased, the proportion of lead should be in the higher range. If it is desirable to increase the strength of the material, a lesser proportion of lead should be utilized. Additional elements may be added for their wellknown enhancement of particular properties such as zinc, tin, nickel, etc., in amounts up to about 10% by weight of the alloy. As to the homogeneity promoter of this invention, it has been found that the elemental carbon component is preferably nely powdered graphite. Although co-arser carbon may be used, the larger particles tend to decrease the efficiency of the process, presumably due to reduced surface area to volume ratio. Other forms of carbon include bone-black, carbon-black, charcoal and the like.

The terms rare earths and rare earth carbonates as used throughout this application are intended to include scandium, yttrium, lanthanum, and the lanthanides, the latter term encompassing those metals having atomic numbers from 58 to 7l. The preferred rare earths are cerium and yttrium and mixtures thereof with lanthanum, praseodymium, neodymium, samarium and europium. The preferred rare earth compounds are the halocarbonates, particularly the uorocarbo-nates of the above metals. The carbonates and oxides of the rare earths are also suitable in this invention.

In addition to the carbon and rare earth compound, an alkali or alkaline earth compound may be present in the homogeneity promoter. 'Ihe alkali metal component compound may be lithium, potassium or sodium (or other metals of Group la of the Periodic Table), preferably combined'as a carbonate. The alkaline earth compound may be calcium, strontium or barium (or other metal of Group lla of the Periodic Table) preferably combined as a carbonate.

The amount of homogeneity promoter used must be at least that amount which ensures formation of a uniformly dispersed mixture of lead and copper which does not segregate on solidification. A preferred effective range of the proportions has been found to be about 1-5 grams of carbon or graphite powder and about 3-15 grams of rare earth compound for each pound of alloy. Below this proportion improvements in homogeneity are obtained, but the effect is less pronounced when a very minor amount of promoter is used. Higher amounts of the homogeneity promoter may be used, for example, up to 10 grams of graphite and 30 grams of the rare earth compo-und for each pound of alloy. Although these and even greater amounts provide an improved alloy in accordance with the present invention, the use of greater amounts from an economic standpoint is less attractive. The maximum proportion of the promoter is determined by characteristic requirements of the alloy, and economic considerations. The amount of alkali or alkaline earth method compound is from 0-30 grams per pound of alloy; but preferably from 2f-l5 grams.

Although the exact mechanism is not completely understood, and patentability is not dependent thereupon, it is believed that the rare earth compound may be partially decomposed to liberate gases which provide a stirring action and nucleation effect and that the undecomposed portion of the promoter also provides nucleation sites. For example, with the preferred cerium fluorocarbonates and graphite, the following reactions may occur:

CeFCO3 CeFO+ C02 The nucleation and possibly agitation prevent gross separation of the load and the copper phases. The nucleation sites cause the final solidified structure to be fine-grained and further allows more efficient and homogeneous entrapment and entrainment of the lead phase in the copper matrix. Also, inoculation occurs by unreacted (or partially reacted) rare earth compound and graphite during stirring of the melt. The inoculation by these particles which are not fully decomposed provides sites for the nucleation and growth of fine lead particles. The combined action promotes a random, fine-grained dispersion of lead in copper which is mandatory for the optimum characteristics and requirements of a bearing alloy. If desired, inert atmospheres may be used to blanket the system.

The process of this invention produces a novel copperlead alloy which has a finer and more uniform dispersion of the lead in the copper. The composition of the alloy is from 5 to 55 percent lead, preferably 20 to 45 percent lead, 95 to 45 percent copper, preferably 80 to 55 percent copper, with up to percent of other metals, preferably zinc and/or tin, with only minor amounts of other metals, and trace amounts of the homogeneity promoter. The preferred average particle size of the lead in the copper matrix is between 0.002 mm. to 0.020 mm. diameter. Larger particles of lead occur but only a very minor amount of segregation occurs, which is not detrimental. An average particles size of 0.002 to 0.010 mm. for copper-lead alloys having to 45 percent lead produces an excellent alloy in accordance with the present invention. The average particle size remains approximately within the above ranges even after the alloy is remelted or recast, although some minor agglomeration does occur.

Another advantage of this process is the remelt capability of the copper-lead alloy without substantial segregation. This effect is desirable particularly if the material is produced as solid billets for use in subsequent castings into desired forms. The remelt capability without undesirable segregation is believed attributed to remnants of the homogeneity promoter remaining in the alloy or may be a function of the iineness of the original dispersion.

Although the homogeneity promoter has a lingering effect in improving the homogeneity of the alloy it may be desirable upon successive remelts, or where the original alloy composition remains molten for an extended period of time, to add the homogeneity promoter in increments. For example, when the alloy remains molten for a period of 10 minutes to an hour, a second addition of the promoter in an amount within the preferred effective range should be made prior to using (i.e., casting) the alloy.

Additional additives may be used in combination with the above-described homogeneity promoter. For example, from l to 10 grams of a metal phosphate may be used, such as ortho lead phosphate, ortho cupric phosphate or ortho tin phosphate.

In one method of making the alloy of the present invention, copper of the desired quantity is placed in a graphite crucible and brought to a temperature of 1250"- l350 C. using an induction heater. When the copper is melted and has attained the appropriate temperature, as for example about 1275 C., the lead and the homogeneity promoter are added to the melt preferably with stirring. The temperature of the mixture is maintained for at least l minute and preferably 3 minutes for best results. The melt is then allowed to cool through its solidification temperature.

The novel alloys of copper-lead prepared by the foregoing method have the structural characteristics required Cil -ilO

to produce optimum anti-frictional qualities. The purity is high since the alloy has been thoroughly deoxidized. The lead phase is finely and randomly dispersed throughout the copper matrix. Thes factors contribute to a low coefficient of friction in the lifetime of the bearing alloy. They also have a high thermal conductivity, and low electrical resistivity. In addition, they may be sintered, drawn, extruded, rolled and machined without losing their superior anti-friction qualities.

The alloy of the present invention is particularly useful as a bearing surface. It is suited for use when high or low temperatures and high stresses are present. Most strandard methods for making bearings and bearing sur faces may be employed. The bearing can be made by castin-g techniques as set forth in greater detail below. Additionally, powder metallurgical techniques are useful. As an example, in bonding the alloy of the present invention to steel, the alloy can be powdered utilizing an atomization method to as fine as 1 micron. The steel is heated, until it turns blue (approximately 600 F.) and the powder made from the alloy is then sprayed onto the steel surface. The heat from the surface of the steel bonds the copper-lead alloy to the steel on contact. The powdered alloy can also be sintered onto a steel backing to provide a thicker bearing surface. The bond is strong enough to resist high stresses that result from bearing forces while providing excellent bearing properties.

Another manner in which the alloy of the present invention can be used is as an additive to lubricants. The alloy is combined in powdered form with other lubricants such as greases and oils in quantities ranging preferably from a trace to 4 ounces per pound of the grease or oil. The resulting combination is a lubricant which fully coats moving parts thereby increasing the life of these parts. Maintenance requirements are also reduced. The alloy is of value when the lubricant combination is used in sealed units where frequent changes of lubricant are uneconomical. In this application, the improved results are obtained over a longer period of time when higher percentages of lead are used in the alloy. The alloys of the present invention may also be of value in ordnance developments, such as for small arms ammunition, rotating bands for larger caliber shells, or on the inside surface of gun barrels.

The alloys of this invention are also suitable for forming powders. The powder may be made directly from the molten alloy by pouring it into a high velocity stream of an inert gas such as nitrogen. Alternatively, the finished alloys of this invention may be remelted and then poured into a high velocity stream of an inert gas. This latter procedure is possible due to the excellent remelt capability of the alloys without any significant loss of the line dispersion of the constituents.

This invention will be illustrated in greater detail by reference to the following embodiments.

EXAMPLE I `68.4 grams of copper were melted in a graphite crucible at 1300 C. with a Lepel induction unit. 45.6 grams of lead were then added to the crucible. 2.28 grams of a commercially available rare earth mixture (Molybdenum Corp.) which was predominantly CeFCO3 and 0.57 gram of powdered graphite were also added to the crucible. The molten batch in the crucible was held at approximately 1300 C. for two minutes while stirring and then poured into a cold (room temperature) graphite crucible and allowed to cool. The resultant ingot was examined visually and by the photomicrographic technique. The ingot showed no lead segregation and had a tine dispersion of the constituents.

The rare earth mixture is known as bleached rare earth tiuorocarbonates, containing predominantly the cerium compound, with minor amounts of lanthanum, praseodymium and neodymium fluorocarbonates and trace amounts of other rare earth uorocarbonates, such as samarium and europium.

EXAMPLE II The procedure of Example I was repeated on a larger scale with 9 pounds of copper, 6 pounds of lead, 123 grams of the same rare earth uorocarbonate mixture and 34 grams of powdered graphite. An excellent dispersion of the lead in the copper was obtained.

A photographic examination of the structure, as illustrated in FIGS. l and 2 shows the fine dispersion of the particles. FIGS. 1 and 2 show magniiications of 50X and 250 respectively.

lThe resultant alloy was tested for hardness and was rated 38.8 on the Brinell scale.

EXAMPLE III The procedure of Example I was repeated with 9 pounds of copper, 6- pounds of lead, 123 grams of the same rare earth fluorocarbonate mixture, 34 grams of powdered graphite, and 68 grams of sodium carbonate. The resultant casting showed a fine dispersion of lead in copper.

The alloy was tested for hardness and was rated 37.0 on the Brinell scale.

EXAMPLE IV For purpose of comparison, the procedure of Example I was repeated with 9 pounds of copper and 6 pounds of lead. The casting showed gross segregation of the lead in the copper. The Brinell hardness test resulted in a rating of 28.4.

EXAMPLE V The procedure of Example I was repeated with 68 grams of copper, 45 grams of lead, 1 gram of a cerium oxide concentrate and 0.8 gram of powdered graphite. The cerium oxide was a concentrate from a mixture of rare earths and contained about 98% cerium oxide.

The resultant alloy showed a good dispersion of lead in copper with little indication of segregation. The alloy was of suitable quality for a bearing material although the dispersion of constituents was not as tine as the product of Example I.

EXAMPLE VI The procedure of Example I was repeated with 68 grams of copper, 45 grams of lead, 1 gram of a cerium oxidecerium carbonate concentrate from a mixture of rare earth oxides and carbonates, and 0.8 gram powdered graphite. The casting obtained showed a good dispersion of lead in copper of a quality comparable to that made by the procedure of Example V. This procedure was repeated on a larger scale with comparable results, using 9 pounds of copper, 6 pounds of lead, 68 grams of the cerium oxide-cerium carbonate concentrate and 34 grams of powdered graphite.

EXAMPLE VII The procedure of Example I was repeated with 68 grams of copper, 45 grams of lead, 4 grams of 98-199% yttrium oxide (Y203) concentrate from a mixture of rare earth oxides, and 0.8 gram of powdered graphite. The resultant alloy had a good dispersion of lead in copper and was of a quality similar to the alloy of Example V.

The term segregation as used in this application is intended to refer to lead particles having a diameter greater than about mm. The alloys of this invention have only a minor amount of segregation, preferably about zero percent. The massive segregation which occurs without the homogeneity promoter of this invention is normally exhibited as a layering of the lead. .Minor segregation is evidenced by lead particles having a size of about 1-2 mm., but this is not a serious problem if such particles are well dispersed and constitute less than 5% of the lead volume.

This invention has been described in terms of specific embodiments set forth in detail. Alternative embodiments will be apparent to those skilled in the art in view of this disclosure, and accordingly such modifications are to be contemplated within the spirit of the invention as disclosed and claimed herein.

What is claimed is:

1. The method of making a homogeneous copper-lead alloy comprising the step of adding an effective amount of a homogeneity promoter to a mixture of molten lead and copper, wherein said mixture comprises from 5-55% lead and from 95-45% copper, and wherein the total of said lead and copper in said mixture is at least and said promoter comprises elemental carbon and a rare earth metal compound selected from the group consisting of oxides, carbonates and halocarbonates.

2. A method according to claim 1 wherein the temperature of said molten lead and copper is maintained in the range of between about 1250l350 C. for at least 1 minute subsequent to said adding step and thereafter including the step of cooling said molten alloy.

3. A method according to claim 1 wherein the proportions of said promoter are from about 1-5 grams carbon and about 3-15 grams rare earth metal compound per pound of alloy.

4. A method according to claim 1 wherein said promoter comprises powdered graphite and cerium fluorocarbonate.

5. A method according to claim 1 wherein said promoter additionally comprises an alkali metal carbonate or alkaline earth metal carbonate.

6. A method according to claim 5 wherein the proportion of said carbonate is from 2-15 grams, for each pound of alloy.

7. A method according to claim 1 wherein said alloy contains up to 10% of a metal selected from the group consisting of tin, zinc and combinations thereof.

8. A method according to claim 1 wherein said alloy comprises from about 20 to 45% lead.

9. A homogeneous alloy comprising a mixture of cop- -per and lead, wherein said mixture comprises from 5-55% lead and from -45% copper, and wherein the total of said lead and copper in said mixture is at least 90%, and trace remanants of the products from a homogeneity promoter in molten copper and lead, said homogeneiety promoter comprising elemental carbon and a rare earth metal compound selected from the group consisting of oxides, carbonates and halocarbonates.

10. The alloy of claim 9 comprising about 5 to 55% lead, and about 95 to 45% copper, wherein the lead is in the form of a tine dispersion in a copper matrix, and the average diameter of said lead particles is between about 0.002 mm. to 0.02 mm.

11. The alloy of claim 9 comprising 20 to 45 lead, wherein the lead is in the form of a fine dispersion in a copper matrix, and the average .diameter of said lead particles is between about 0.002 mm. to 0.01 mm.

12. A bearing wherein the surface of said bearing coinprises the alloy made by the process of claim 1.

References Cited UNITED STATES PATENTS 3,556,779 1/1971 Turkisher 75-135 2,802,733 8/1957 Bungardt 75-163 X y2,229,117 1/1941 Ness 75-163 3,158,470 11/1964 Burghoff et al. 75-153 X 3,253,910 5/196'6 Burghoff et al 75-153 X OTHER REFERENCES Foundry, October 1962, pp. 46 and 47.

CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R.

75-134, 163, 166; 308-241, DIG. 8 

